1. Field of the invention
The present invention relates to an improvement of a swirl chamber type combustion chamber for a diesel engine in which a stream of combustion gas is injected from a swirl chamber to a main combustion chamber so as to spread out right and left.
2. Prior Art
A basic construction of a swirl chamber type combustion chamber for a diesel engine, which being concerned in the present invention, is as described hereinafter. Referring to FIG. 3, at an offset position relative to a main combustion chamber 1 in a diesel engine, there is provided a swirl chamber 3 which is in communication with the main combustion chamber 1 through an injection passage 2, the axis 4 of which is directed in such an oblique direction as it gets near the center of the main combustion chamber as progressing from the swirl chamber 3 to the main combustion chamber 1. The injection passage 2 is formed in such a shape as it spreads the right and left portions of the stream of combustion gas expanded in the swirl chamber 3, at a spread angle towards the main combustion chamber.
Generally, it is known in the art that an injection passage which is simply formed in a cylindrical shape can not enhance a specific air utilization in the swirl chamber type combustion chamber because the combustion gas stream doesn't spread so widely in the main combustion chamber 1 when it is injected thereinto through the passage 2 from the swirl chamber 3.
Therefore, the applicant( the assignee ) of the present invention has disclosed in Japanese Patent Publication of No. 59410 of 1982 an improved injection passage that is formed in such a shape as it spreads gradually at the both sides thereof towards the main combustion chamber 1 like a diffuser in order to enhance the diffusion of the combustion gas stream and then the specific air utilization. That is, the injection passage 2 comprises a round through hole and a pair of swelled side channels connected thereto on both sides thereof. Accordingly, the injection passage 2 is adapted to produce a main stream of combustion gas along the axis 4 thereof as well as right and left sub-streams of combustion gas spread out to both sides of the main stream like an unfolded fan when the combustion gas stream is injected onto a flat top surface of a piston head ascended near the top dead center in order that the specific air utilization may be enhanced.
On the other hand, in order to enhance the swirl mixing efficiency in the swirl chamber, since it is necessary that the volume of the swirl chamber 3 might be enlarged possibly and that of the main combustion chamber 1 might be reduced possibly, the top clearance above the piston is narrowed extremely at the top dead center of the piston.
Thereupon in the above-mentioned prior art, the injection passage 2 is almost closed by the flat top surface of the piston while the piston passes by the top dead center thereof. Hence, it becomes impossible owing to the large resistance at the outlet of the injection passage 2 for the stream of combustion gas expanded in the swirl chamber 3 to flow smoothly, properly and forwardly into the main combustion chamber 1, and further the stream of combustion gas injected thereinto is apt to be disturbed by the excessive spread thereof to both right and left sides, for example over an angle of ab. 120 degree in comparison with an ideal spread angle of 60 degree at the top dead center of the piston. Thus, since the stream of combustion gas can't mix uniformly with air which exists in a forward portion thereof, the operating characteristics of the engine, such as, for example, power and specific fuel consumption are made worse owing to the poor air utilization.
Further, since the fuel-air mixture in the right and left portions of the combustion gas stream generated by the excessive spread thereof becomes too rich to ensure the complete combustion, carbon deposits produced there are apt to cause piston-ring stickings or scuffings. Moreover, since the positions where the carbon deposit is produced are near the sliding surfaces of the piston and the cylinder, the deposit is apt to drop therebetween and cause sticking. And since the stream of combustion gas is obstructed as described above and the portions adjacent to the injection passage are heated locally so as to cause uneven heating in the combustion chamber, thermal strains are apt to be generated in the piston.